What is the difference between echo and Write-Host in PowerShell?

I'm confused about the difference between echo and Write-Host in PowerShell. I have two files, POC.ps1 & validatePath.ps1. These files are on my local machine, and I'm running them on a remote machine using Invoke-Command. I am using PowerShell v3.0.

To execute both of these scripts I use the command:

.\POC.ps1 -filename C:\Users  -user Blaine

Here are the two files:

POC.ps1:

param($filename, $user)

echo $filename
echo "This"
echo $user

$responseObject = Invoke-Command testcomputer -FilePath .\validatePath.ps1  -ArgumentList($filename, $user) -AsJob

while($responseObject.State -ne "Completed")
{

}

$result = Receive-Job -Id $responseObject.Id -Keep
echo $result

Here is where things get weird...

validatePath.ps1:

Param([string] $filename,
      [string] $user)

function ValidatePath( $filename, $user, $fileType = "container" )
{
    Write-Host "This is the file name: $filename"
    Write-Host "This is user: $user"  <--- Notice I'm using Write-Host here
    $fileExist = $null
    if( -not (test-path $filename -PathType $fileType) )
    {
        throw "$user, the path $filename does not exist!"

    }
    else
    {
         Write-Host "This is the second part"
         echo $filename found!
    }
    Write-Host "This is the third part"
    return $fileExist
}


try
{

    ValidatePath($filename, $user)
}
catch
{
    $e = $_.Exception
    echo $e
}

When I run the above script, this is the output:

C:\Users
This
Blaine
This is the file name: C:\Users Blaine
This is user:  <--- Notice where this line is?
This is the second part
This is the third part
C:\Users
Blaine
found!

But if I change the validatePath.ps1 to this:

Param([string] $filename,
      [string] $user)

function ValidatePath( $filename, $user